Tray



Oct. 1, 1968 w, DONOVAN 3,403,834

TRAY

Filed July 11, 1966 FIG. I a

F/G. I /6 1 L 42. 54 haw-'4 F/& H

INVENTOR. D. W. DONOVAN ATTORNEY United States Patent 3,403,834 TRAY Donald W. Donovan, Glastonbury, Conn., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed July 11, 1966, Ser. No. 564,131 7 Claims. (Cl. 229-2.5)

ABSTRACT OF THE DISCLOSURE A tray having improved bend resistance provided by a plurality of substantially parallel, intersecting primary and secondary ribs integral with, and extending across the body of the tray.

The present invention relates to a tray and more particularly relates to a tray having improved resistance to bendmg.

The use of trays to transport or carry items is well known. In recent years trays have been used as a package for consumer items such as candies, meats, vegetables, etc. The assembly of items in a tray permits easy examination of the contents by a potential purchaser. Unfortunately, the use of these trays has been limited primarily by their weight and by the cost of the material used for their construction. On the other hand, reduction of the material used to make the tray generally tended to make the tray too weak or susceptible to bending particularly when the tray is held along one edge or when being overwrapped with film material. It has now been found that a tray can be formed from a rather limited amount of material having superior structural characteristics resulting from a rather unique tray design. r

Accordingly, it is a principal object of the present invention to provide a tray having improved structural properties.

It is another object of the present invention to provide a tray strong enough to contain relatively heavy items while employing a minimum of material for its construction.

It is another object of the present invention to provide a tray having improved resistance to bending particularly when the tray is held along one edge and/or when supporting a comparatively heavy item.

It is a further object of this invention to provide method and means to carry out the above objects.

Other objects of this invention will in part be obvious and will in part appear hereinafter.

These and other objects are attained by a novel tray of generally uniform thickness formed to have a plurality of substantially parallel primary ribs extending across said tray and a plurality of substantially parallel secondary ribs, portions of which blend into the sides of said primary ribs and other portions of which extend into the side and over the top of said primary ribs.

FIG. I is a top plan view of a tray.

FIG. II is a side view of a portion of the rib taken along the section 22 of FIG. I.

FIG. III is a side view of a portion of the rib taken along the section 33 of FIG. I.

FIG. IV is a top view of an embodiment of the present invention.

Referring to the drawings and more particularly FIGS. IIII, there is schematically shown a tray of generally uniform thickness formed to have a plurality of primary ribs 12 extending from edge 14 to edge 16 and a plurality of secondary ribs 18 which extend across the bottom of tray 10 from edge 20 to edge 22.

FIG. II illustrates a side view of rib 12 taken along the line 22 of FIG. I. In the illustration of FIG. I, the

3,403,834 Patented Oct. 1, 1968 rib 12 extends into the lower portion 24 of the side 26 of transverse rib 18.

FIG. III illustrates the side view of the same rib 12 taken along the section 33 of FIG, I wherein rib 12 slopes up to a level or peak above secondary rib 18b shown extending into the side of rib 12. In some-respect the design as described above may be likened to a weave except that the ribs are an integral part of the tray as opposed to divisible parts or strands.

FIG. IV illustrates a top view of an embodiment wherein the top portion of a rib 30 flattens out as it extends into the side 32 of a transverse rib 34. The flattening of the rib in this manner tends to enhance the structural stability of the design, although unusually good structural stability is attained even without the flattened rib.

The above description and particularly the drawings are set forth for the purpose of illustration only and not for the purpose of limitation. Although the illustrated embodiment is a tray of a rectangular shape, it is made obvious that the tray may be of varied shapes, for example, square, oval, round and the like.

As earlier indicated, the present invention is directed a novel tray of generally uniform thickness formed to have a plurality of substantially parallel primary ribs extending across said tray and a plurality of substantially parallel secondary ribs, portions of which blend into the sides of said primary ribs, and other portions of which extend into the side and over the top of said primary ribs. Although it is possible to shape the primary and secondary ribs differently, it is generally preferable for the attainment of a balanced structure to shape them similarly, that is the primary ribs also being designed such that portions of the ribs will blend into the sides of the secondary ribs and other portions will extend into the side and over the top of the secondary ribs.

This rather unique design results in unusual structural properties capable of holding relatively heavy objects without bending even though the tray may be constructed of thin gauge and/or semi-flexible materials. The configuration illustrated in FIGS. II and III may be likened to a weave except that it is integrally formed. To attain maximum stability and optimum structural properties, certain critical dimensional relationships have been developed. These relationships may be more easily described by reference to FIG. II wherein it describes the height of rib 18 and b the height of rib 12 assuming that rib 12 connects into the side of rib 18 along a straight line extension (see dashed line) of top edge 40 of rib 12. It has been found that optimum structural characteristics are attained when:

h axht and wherein the constant a ranges between 0.1 to 0.9.

It appears that the relationship of h to h is the most important, although another contributing factor has been found to lie in the relationship of the base w of the rib 18 to its height h, This relationship can be defined as:

wherein the constant b may range anywhere between 0.1 and 3.0. Also of significance is the angle alpha between the extension of the top surface 40 of rib 12 and the side 26 of rib 18. The optimum angle generally ranges between 20 to As a practical matter the rib 12 is not usually designed to connect rib 18 in a straight line which extends from along the edge 40 but rather is rounded such that it tends to intersect rib 18 at a point somewhere above where the extension of the edge 40 would ordinarily connect rib 18. However, for purposes of clear definition, h is measured at a point along the side of rib 18 determined by assuming the top edge 40 of rib 12 extends in a straight line into rib 18.

The above description refers specifically to the relationship between intersecting ribs. However, the relationship of an intersection has a bearing on the relationship of other intersections. For example, the height h as defined for one intersection can extend up to two times the height of an adjacent intersection with good structural results being obtained.

In addition, referring to FIG. IV, the base line 42a may extend parallel to its opposite base line 4211 into the bottom edge of rib 18 or may even extend in relation to its opposite base line into rib 18 in a converging or a diverging manner although the parallel arrangement is generally preferred.

As indicated previously the structural stability and strength of the present tray can be enhanced by flattening the top of the rib as it extends into the side of a crossing rib as illustrated in FIG. IV.

The term flattening as used herein refers to any significant reduction in the slope across the rib occurring at an approximately axially extending edge such as edges 44a and 44b shown in FIG. IV. Thus a change in curvature across the rib is includable in the flattening term as used herein. In practice, the same change in slope occurs on both sides of the rib thereby producing the flattening effect. The extent of the flattening or slope change is measured by the disttance between point of slope change or edges on both sides of the rib at the intersection with the crossing rib regardless of the curvature between the points. In FIG. IV, this distance is measured between edges 44a and 4417 where rib 30 intersects rib 34 and is designated as x. The distance x or extent of flattening bears a relationship to y the distance between opposing base lines (see above) and optimum results are obtained where:

wherein the constant d is equal to 0.1 to 1.

Referring again to FIG. II, the optimum distance between adjacent ribs 18 has been found to be relatable to function of the gauge of the tray and the material of construction. For rigid and semi-rigid plastic trays useful in the packaging of relatively small items, i.e., trays having an overall bottom surface area ranging between 4 to 200 square inches, the thickness is generally set as a practical matter to range between 3 thousandths of an inch to 40 thousandths of an inch. Within these ranges of material, bottom surface area and thickness, the optimum distance between opposing edges of adjacent ribs ranges between 0.5 to 3 inches.

The materials used for the construction of the above described trays can vary considerably as long as they are capable of being formed to conform to the design parameters set forth above. Preferred materials are rigid and semi-rigid plastics such as polyolefins, for example, polyethylene or isotactic polypropylene; styrene copolymers, for instance, styrene-acrylonitrile copolymers; polyacrylates, polymethacrylates; polycarbonates; polyvinyl chloride; and polyethylene terephthalates. Particularly, preferred is biaxially oriented polystyrene.

The tray of the present invention can be readily molded from sheet material utilizing any of the conventional molding techniques, for example, vacuum, punch and die, positive pressure and the like. In the case of the preferred plastic material, biaxially oriented polystyrene referred to above, the forming operation is generally carried out at temperatures ranging anywhere from 175 to 400 F. utilizing differential pressures to form the sheet material against the wall of a die contoured to effect the design described above.

In general, the present tray finds particular utility for the packaging of various consumer items such as candies, meats, vegetables, etc. In most instances, when used in this manner, an overwrap which may be of transparent plastic is employed to protect the contained items from detrimental effects of exposure to the environments. Furthermore, the package has unique adaptibility to high speed forming operations.

The above description and particularly the drawings are set forth for purposes of illustration only. Many variations and modifications thereof will be obvious to those skilled in the art and can be made without departing from the spirit and scope of the invention herein described.

What is claimed is:

1. A novel tray of generally uniform thickness formed to have a plurality of substantially parallel primary ribs extending across said tray and a plurality of substantially parallel secondary ribs, portions of which blend into the sides of said primary ribs and other portions of which extend into the side and over the top of said primary ribs, each of said secondary rib portions which blends into the side of a primary rib having a height represented by I1 with h representing the height of said primary rib at the intersection of said primary and secondary ribs, and which relationship corresponds to the formula:

wherein the constant a ranges between 0.1 to 0.9, each of said primary ribs at the point of intersection with a secondary rib also having a base represented by w, and a relationship which corresponds to the formula:

wherein the constant b may range anywhere between 0.1 to 3.0.

2. The tray according to claim 1 wherein the tops of said portions of said secondary ribs which blend into the sides of said primary ribs are flattened.

3. The tray according to claim 1 wherein the tray is of generally rectangular shape.

4. A novel tray of generally uniform thickness formed to have a plurality of substantially parallel primary ribs extending across said tray and a plurality of substantially parallel secondary ribs, portions of which blend into the sides of said primary ribs and other portions of which extend into the side and over the top of said primary ribs, said primary ribs also being designed such that portions of the primary ribs will blend into the sides of said secondary ribs and other portions will extend into the sides and over the tops of said secondary ribs, each of said secondary rib portions which blends into the side of a primary rib having a height represented by h with h representing the height of said primary rib at the intersection of said primary and secondary ribs, and which relationship corresponds to the formula:

wherein the constant a ranges between 0.1 to 0.9, each of said primary ribs at the point of intersection with a secondary rib also having a base represented by w, and which relationship corresponds to the formula:

wherein the constant b may range anywhere between 0.1 to 3.0.

5. The tray according to claim 4 wherein the angle between the top surface of the secondary rib and the side of said primary rib ranges between 20 to and the distance between opposing edges of adjacent ribs ranges between 0.5 to 3 inches.

6. A novel tray of generally rectangular shape, having a generally uniform thickness of between 3 to 40 thousandths of an inch, and an overall bottom surface area ranging between 4 to 200 square inches, said tray being formed to have a plurality of substantially parallel primary ribs extending across said tray, and a plurality of substantially parallel secondary ribs, portions of which blend into the sides of said primary ribs and other portions of which extend into the sides and over the top of said primary ribs, said primary ribs also being designed such that portions of the primary ribs will blend into the sides of said secondary ribs and other portions will extend into the sides and over the top of said secondary ribs, each of said secondary rib portions which blends into the side of a primary rib having a height represented by I2 with h representing the height of said primary rib at the intersection of said primary and secondary ribs, and which relationship corresponds to the formula:

wherein the constant b may range anywhere between 0.1 to 3.0.

7. The tray according to claim 5 wherein said tray is constructed of biaxially oriented polystyrene.

References Cited UNITED STATES PATENTS 2,407,079 9/1946 Howard 22021 2,918,379 12/1959 Lurie 2292.5 2,936,922 5/1960 Williams 229-2.5 X 2,967,654 1/1961 Palmer 229-35 3,281,003 10/1966 Pesut 229-2.5 3,306,484 11/ 1966 Padovini 2292.5 X

DAVIS T. MOORHEAD, Primary Examiner. 

